Methods of reverse link power control

ABSTRACT

Methods of reverse link power control are provided. A first example method includes first measuring a first type of interference, second measuring a second type of interference, determining a ratio between the first and second measurements and broadcasting the determined ratio to a plurality of mobile units. A second example method includes receiving a broadcasted ratio indicating a ratio between two different types of interference and calculating a power level for reverse link transmissions based on the received broadcasted ratio. A third example method includes first adjusting OFDMA transmission power based on first feedback signals during an OFDMA transmission and second adjusting OFDMA transmission power based on second feedback signals during periods between OFDMA transmissions. A fourth example method includes receiving a plurality of interference indicating signals from different base stations and determining whether to adjust a maximum transmit power threshold based on the plurality of interference indicating signals, the maximum transmit power threshold indicating the maximum permitted transmission power level below which transmissions are constrained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Example embodiments of the present invention relate generally tocommunications systems, and, more particularly, to wirelesscommunication systems.

2. Description of the Related Art

Conventional wireless communication systems include one or more basestations or base station routers, which may also be referred to asaccess points, node-Bs or access networks, for providing wirelessconnectivity to one or more mobile units, which may also be referred tousing terms such as user equipment, subscriber equipment, and accessterminals. Examples of mobile units include cellular telephones,personal data assistants, smart phones, text messaging devices,laptop/notebook computers, desktop computers and the like. Each basestation may provide wireless connectivity to one or more mobile units,such as the mobile units in a geographical area, or cell, associatedwith the base station. Alternatively, a base station router may be usedto provide wireless connectivity to the mobile units.

Messaging sent from a base station or base station router to one or moremobile units is generally referred to as “forward link” or “downlink”messaging. Messaging sent from a mobile unit to a base station or basestation router is generally referred to as “reverse link” or “uplink”messaging.

Orthogonal frequency division multiplexing (OFDM) is an efficientmodulation scheme for signal transmission over frequency-selectivechannels. In OFDM, a wide bandwidth is divided into multiple narrow-bandsub-carriers, which are arranged to be orthogonal with each other. Thesignals modulated on the sub-carriers are transmitted in parallel.

OFDM may be used to support multiple access for multiple subscribersthrough time division multiple access (TDMA), in which each subscriberuses all the sub-carriers within its assigned time slots. Orthogonalfrequency division multiple access (OFDMA) is another method formultiple access, using the basic format of OFDM. In OFDMA, multiplesubscribers simultaneously use different sub-carriers, in a fashionsimilar to frequency division multiple access (FDMA) (e.g., for each“shared” sub-carrier, frequency divisions are used to allow multipleaccess).

OFDMA divides a signal into sub-channels (i.e., groups of carriers),with each sub-channel being allocated to a different subscriber.Different sub-channels may then be combined from various carriers. Eachsubscriber can be treated separately, independent of location, distancefrom the base station, interference and power requirements. Variousmodulations can be used for each of the carriers in the system toprovide improved coverage and throughput. The sub-channel structure ofthe OFDMA enhancement enables more efficient duplexing techniques, suchas Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD),and creates a signal with reduced interference and capable of higherdata throughput. In FDD systems, both forward link and reverse linktransmissions occur simultaneously on different carriers.

FIG. 1 illustrates a conventional OFDMA system 100. As shown in FIG. 1,the OFDMA system 100 includes a plurality of user equipments (UEs) 105in communication with one or more serving Node Bs 120/125 over an airinterface. The plurality of Node Bs are connected to a radio networkcontroller (RNC) 130 with a wired interface. Alternatively, while notshown in FIG. 1, the functionality of both the RNC 130 and Node Bs120/125 (alternatively referred to as “base stations”) may be collapsedinto a single entity referred to as a “base station router”. The RNC 130accesses an internet 160 through a gateway support node (GSN) 150 and/oraccesses a public switched telephone network (PSTN) 170 through a mobileswitching center (MSC) 140.

FIG. 2 illustrates a transmitter 200 in a conventional OFDMA system. Inan example, the transmitter 200 of FIG. 2 is employed within atransmitting entity (e.g., Node B 120/125, UE 105/110, etc.) within theconventional OFDMA system 100 of FIG. 1.

As shown in FIG. 2, the transmitter 200 includes a modulator 210, aserial-to-parallel (S2P) converter 220, an Inverse Fast FourierTransformer (IFFT) module 230, a cyclic prefix inserter 240 and a timedomain filter 250. The IFFT module 230 includes N ports for receivingmodulation symbols. Each of the N ports is associated with an orthogonalsub-carrier. IFFT module 230 is operable to use an NxN IFFT matrix toperform transform operations on its inputs, wherein the entries of thematrix F_(j,k) are defined as F_(j,k)=e−2^(πijk/n), j,k=0,1,2, . . .,n−1 and i=√{square root over (−1)}.

Encoded data symbols are provided as input to modulator 210. Modulator210 uses well-known modulation techniques, such as BPSK, QPSK, 8 PSK, 16QAM and 64 QAM, to convert the encoded data symbols into K modulationsymbols Sk which are then provided as input to S2P converter 120, whereK≦N. The S2P converter 220 outputs parallel streams of modulationsymbols, which are provided as inputs to one or more of the N ports ofthe IFFT module 230 associated with orthogonal sub-carriers over whichthe encoded data symbols are to be transmitted. In the IFFT module 230,an inverse fast Fourier transformation is applied to the modulationsymbols Sk to produce a block of chips cn, where n=0, . . . ,N−1. Thecyclic prefix inserter 240 copies the last Ncp chips of the block of Nchips and prepends them to the block of N chips producing a prependedblock. The prepended set is then filtered through time domain filter 250and subsequently modulated onto a carrier before being transmitted.

OFDMA systems provide reduced interference and higher data rates on thereverse link, as compared to conventional Code Division Multiple Access(CDMA), due to the in-cell orthogonality property of OFDMAtransmissions. However, OFDMA comes at the cost of increased signalingand a failure to provide bandwidth sharing for users transmitting atlower data rates and/or requiring fast access to a carrier. In contrast,CDMA systems allow multiple subscriber access without explicitrequest-and-grant mechanisms, as present in conventional OFDMA, and thismay increase user access to the carrier for transmissions.

Power control is a critical problem for the reverse link in CDMA systemsbecause CDMA systems may experience significant in-cell and outer-cellinterference. OFDMA systems typically experience less in-cellinterference than CDMA systems due to the orthogonality property ofOFDMA, and thereby OFDMA systems may employ “looser” power controlrequirements since interference present in an OFDMA system may besubstantially limited to outer-cell interference. However, reverse linkpower control in OFDMA systems remains a problem in conventional OFDMAsystems not withstanding the lesser in-cell interference. For example,effective rate control on the reverse link in OFDMA systems may bedifficult to achieve without a reverse link transmission power toreverse link data rate mapping.

Since OFDMA transmissions are scheduled by the base-station by givingdifferent portions of available bandwidth to different users, thetransmissions per user are typically “bursty” by nature. Accordingly, itis inefficient to maintain a constant pilot transmitted by all users forperforming closed loop OFDMA power control. On the other hand, purelyopen loop power control techniques are limited in their efficiency sinceopen loop power control techniques typically do not maintain a tightcontrol of outer-cell interference, and a prediction of a receivedsignal-to-interference+noise ratio (SINR) for a given transmit power isless accurate. Accordingly, because OFDMA systems do not transmitcontinuous pilot signal transmissions, it is more difficult to controlreverse link transmission power at all users within the cell becausereverse link power control must be performed individually for each user.

SUMMARY OF THE INVENTION

An example embodiment of the present invention is directed to a methodof controlling reverse link transmission power in a wirelesscommunications network, including first measuring a first type ofinterference, second measuring a second type of interference,determining a ratio between the first and second measurements andbroadcasting the determined ratio to a plurality of mobile units.

Another example embodiment of the present invention is directed to amethod of controlling reverse link transmission power in a wirelesscommunications network, including receiving a broadcasted ratioindicating a ratio between two different types of interference andcalculating a power level for reverse link transmissions based on thereceived broadcasted ratio.

Another example embodiment of the present invention is directed to amethod of controlling reverse link transmission power in a wirelesscommunications network, including first adjusting OFDMA transmissionpower based on first feedback signals during an OFDMA transmission andsecond adjusting OFDMA transmission power based on second feedbacksignals during periods between OFDMA transmissions.

Another example embodiment of the present invention is directed to amethod of determining a maximum permitted transmission power level,including receiving a plurality of interference indicating signals fromdifferent base stations and determining whether to adjust a maximumtransmit power threshold based on the plurality of interferenceindicating signals, the maximum transmit power threshold indicating themaximum permitted transmission power level below which transmissions areconstrained.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only, wherein like referencenumerals designate corresponding parts in the various drawings, andwherein:

FIG. 1 illustrates a conventional OFDMA system.

FIG. 2 illustrates a transmitter in the conventional OFDMA system ofFIG. 1.

FIG. 3 illustrates hybrid OFDMA/CDMA system according to an exampleembodiment of the present invention.

FIG. 4 illustrates a bandwidth allocation for the hybrid OFDMA/CDMAsystem of FIG. 3 according to an example embodiment the presentinvention.

FIG. 5 illustrates a schematic diagram of a transmitter in the hybridOFDMA/CDMA system of FIG. 3 according to an example embodiment of thepresent invention

FIGS. 6A and 6B illustrate an OFDMA reverse link power control processaccording to another example embodiment of the present invention.

FIG. 7 illustrates an OFDMA reverse link power control process accordingto another example embodiment of the present invention.

FIG. 8 illustrates a process of establishing a maximum transmit powerper tone threshold for a mobile station's transmissions according to anexample embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In order to better understand the present invention, a hybrid CodeDivision Multiple Access (CDMA)/Orthogonal Frequency Division MultipleAccess (OFDMA) system according to an example embodiment of the presentinvention will be described first. Then, an example of controlling OFDMAreverse link power in the example hybrid CDMA/OFDMA system will begiven, followed by a method of establishing a maximum power level atwhich mobile station's may transmit within the hybrid OFDMA/CDMA system.

Hybrd CDMA/OFDMA System

FIG. 3 illustrates a wireless communications system (hereinafter “hybridOFDMA/CDMA system”) 300 according to an example embodiment of thepresent invention. As shown in FIG. 3, the OFDMA system 300 includes aplurality of user equipments (UEs) 305 in communication with one or moreserving Node Bs 320/325 over an air interface. The plurality of Node Bsare connected to a radio network controller (RNC) 330 with a wiredinterface. Alternatively, while not shown in FIG. 3, the ftmctionalltyof both the RNC 330 and Node Bs 320/325 (alternatively referred to as“base stations”) may be collapsed into a single entity referred to as a“base station router”. The RNC 330 accesses an internet 360 through agateway support node (GSN) 350 and/or accesses a public switchedtelephone network (PSTN) 370 through a mobile switching center (MSC)340.

While the hybrid CDMA/OFDMA system 300 of FIG. 3 superficially resemblesthe OFDMA system 100 of FIG. 1, the hybrid CDMA/OFDMA system 300 of FIG.3 is further operable to communicate OFDMA type signals over a set ofdynamically assigned orthogonal sub-carriers and CDMA type signals overa set of pre-allocated orthogonal sub-carriers, wherein OFDMA typesignals are signals generated in accordance with well-known OFDMAtechniques and CDMA type signals are signals generated in accordancewith well-known CDMA techniques.

In an example, the CDMA type signals are transmitted over pre-allocatedorthogonal sub-carriers and, thus, do not require the dynamic assignmentof orthogonal resources (e.g. sub-carriers). The CDMA type signals maybe signals associated with users with bursty and periodic trafficpatterns. As will now be described, the hybrid OFDMA/CDMA system 300 maybe a multi-carrier system in which available bandwidth is divided into aset of orthogonal sub-carriers.

FIG. 4 illustrates a bandwidth allocation 400 for the hybrid OFDMA/CDMAsystem 300 of FIG. 3 according to an example embodiment the presentinvention. In the example embodiment of FIG. 4, available bandwidth isdivided into a set of orthogonal sub-carriers. The set of orthogonalsub-carriers are categorized into two groups. The first group, referredto herein as OFDMA group, includes orthogonal sub-carriers used for thetransmission of OFDMA signals. The second group, referred to herein asCDMA group, includes orthogonal sub-carriers used for the transmissionof CDMA type signals. The OFDMA and CDMA groups include one or moresub-groups referred to herein as OFDMA and CDMA zones, respectively.Each zone includes at least one orthogonal sub-carrier. In an example,the CDMA zones are non-adjacent to each other and distributed at evenintervals among the bandwidth allocation 400 with intervening OFDMAzones. In another example, two or more of the CDMA zones are adjacent toeach other. In yet another example, the CDMA zones occupy the entirebandwidth (e.g., an entirety of the bandwidth allocation 400) such thatno bandwidth is reserved for OFDMA zones.

In the example embodiment of FIG. 4, a traffic channel includingorthogonal sub-carriers in the OFDMA group is referred to hereinafter asan OFDMA traffic channel, whereas a traffic channel including orthogonalsub-carriers in the CDMA group is referred to hereinafter as an CDMAtraffic channel. As mentioned earlier, the OFDMA type signals aresignals generated in accordance with well-known OFDMA techniques, andCDMA type signals are signals generated in accordance with well-knownCDMA techniques. In another example, OFDMA type signals may be signalsgenerated in accordance with the well-known Interleaved FrequencyDivision Multiple Access (IFDMA) technique, and/or any type of techniquefor generating signals over a Frequency Division Multiple Access (FDMA)system. Similarly, the CDMA type signals may be generated in accordancewith only CDMA techniques, and/or with CDMA and IFDMA techniques.

FIG. 5 illustrates a schematic diagram of a transmitter 500 according toan example embodiment of the present invention. In an example, thetransmitter 500 of FIG. 5 may be employed within a transmitting entity(e.g., Node B 320/325, UE 305/310, etc.) within the hybrid CDMA/OFDMAsystem 300 of FIG. 3.

In the example embodiment of FIG. 5, the transmitter 500 includes afirst portion 580 for processing CDMA type signals, and a second portion590 for processing OFDMA type signals. The first portion 580 includesmultipliers 505, 510, 515, 520, a summer 525, a serial-to-parallel (S2P)converter 530, K pre-coders 535, an Inverse Fast Fourier Transform(IFFT) module 550, a cyclic prefix inserter 560, and a time domainfilter 570. The second portion 590 includes a modulator 540, a S2Pconverter 545, an IFFT module 550, a cyclic prefix inserter 560 and atime domain filter 570. The pre-coders 535 are configured to use aDiscrete Fourier Transform (DID matrix and/or a matrix based on afrequency domain channel to perform a transform operation on its inputs.Each pre-coder 535 includes Nz output ports. The IFFR module 550 isconfigured to use an IFFF matrix to perform a transform operation on itsinputs. The IFFT module 550 includes NFFT input ports, wherein the NFFTinput ports include KxNz ports associated with orthogonal sub-carriersbelonging to CDMA zones, and NFFT-KxNz input ports associated withorthogonal sub-carriers belonging to OFDMA zones.

In the example embodiment of FIG. 5, in the first portion 580, pilotsymbols and encoded data symbols are provided as inputs into multipliers505, 510. The pilot and encoded data symbols are spread using spreadingcodes, such as Walsh codes, with spreading factors Ncp and Ncd,respectively. In an example, the spreading factor Ncp is equal to Nz,which is a number of CDMA zones in the bandwidth allocation 400 of thehybrid OFDMA/CDMA system 300. The spread pilot and data symbols aresubsequently scrambled in multipliers 515, 520 using a pilot and a datascrambling code, such as Pseudo-random Noise (PN) codes, to producepilot and data chips, respectively, wherein the scrambling codes have aperiod N and N>>Ncp, Ncd. In an example, the scrambling codes may beCDMA zone specific. In another example, the scrambling codes may havedifferent offsets for the pilot and data branches of the first portion580.

In the example embodiment of FIG. 5, the pilot and data chip streams arecode multiplexed in the summer 525 to produce a code multiplexed signal,wherein the code multiplexed signal includes KxNz code multiplexedchips. In another example, the pilot and data chip streams are timemultiplexed. A CDMA type signal may be construed to be the code or timemultiplexed chip signal or any signal derived from the code or timemultiplexed chip signal.

In the example embodiment of FIG. 5, the code multiplexed signal isprovided as an input to the S2P converter 530. The S2P converter 530distributes the code multiplexed chips equally among each of the Kpre-coders 535. In an example, the code multiplexed chips may beprovided as a block of Nz code multiplexed chips. For example, the firstNz code multiplexed chips are provided as an input to the firstpre-coder 535, the next Nz code multiplexed chips are provided as aninput to the second pre-coder 535, and so on. In another example, theS2P converter 530 may distribute the code multiplexed chips unevenly orunequally among K or less pre-coders 535, and the block of codemultiplexed chips may be a size different from Nz.

In the example embodiment of FIG. 5, the pre-coders 535 may use a matrixto perform a transform operation to transform an input vector in thetime domain into an output vector in the frequency domain. In anexample, both the input and output vectors of pre-coders 535 include thesame (e.g., Nz) elements or chips. In another example, the pre-coders535 are Discrete Fourier Transformers (DFT) that use a DFT matrix F ofsize NzxNz to transform the input vector including Nz code multiplexedchips from the time domain to the frequency domain. The entries formatrix F may be expressed asF _(j,k) =e ^(−i2πjk1N) ^(z)   Equation 1wherein j,k=0,1,2, . . . , n−1 and i=√{square root over (−1)}. If thecode multiplexed chips at the input of DFT pre-coder are defined asvector s, where s=[s1,s2,s3, . . . ,sNz]^(T) and T denotes the transposeoperation, the output of DFT pre-coder can be defined as vector x, whichis expressed as $\begin{matrix}{x = {{\frac{1}{\sqrt{N_{z}}}{Fs}} = \lbrack {x_{1},\ldots\quad,x_{N_{z}}} \rbrack^{T}}} & {{Equation}\quad 2}\end{matrix}$wherein Nz denotes the number of pre-coded elements or chips.

In another example embodiment of the present invention, referring toFIG. 5, the pre-coders 535 may use an identity matrix to transform thecode multiplexed chips into the frequency domain from the time domain.Additionally, the pre-coders 535 may use a matrix which is channelsensitive allowing for pre-equalization techniques to be applied to thetransformation.

In the example embodiment of FIG. 5, each of the Nz output ports of theK pre-coders 535 are separately mapped to ports of IFFT 550 associatedwith orthogonal sub-carriers belonging to CDMA zones. In an example, themapping of the Nz output ports to the input ports of IFIFT module 550may be reconfigurable based on which of the orthogonal sub-carriers theCDMA type signals are scheduled for transmission.

In the example embodiment of FIG. 5, in the second portion 590, encodeddata symbols are modulated by the modulator 540 using well-knownmodulation techniques, such as BPSK, QPSK, 8 PSK, 16 QAM, 64 QAM, etc.,to convert the data symbols into K modulation symbols Sk which are thentransferred to the S2P converter 545, wherein K≦N. The S2P converter 545outputs parallel streams of modulation symbols which are provided asinputs to one or more ports of the IFFT module 550 associated withorthogonal sub-carriers over which the encoded data symbols are to betransmitted.

In the example embodiment of FIG. 5, in the IFFT module 550, an inversefast Fourier transformation is applied to the modulation symbols Sk andto pre-coded chips (e.g., output of the pre-coder 535) to produce ablock of chips c_(n), wherein n=0, . . . , NFFT-1. The cyclic prefixinserter 560 copies the last N_(cp) chips of the block of NFFT chips andprepends them to the block of NFFT chips producing a prepended block.The prepended set is then ifitered through time domain filter 570 andsubsequently modulated onto a carrier before being transmitted.

CDMA Reverse Link Power Control

Examples of CDMA reverse link control processes are described in USPatent Application UNKNOWN#, entitled “METHODS OF REVERSE LINK POWERCONTROL”, filed concurrently with this application by the inventors ofthe subject application, hereby incorporated by reference in itsentirety. Accordingly, a further description of CDMA reverse link powercontrol processes has been omitted except as is relevant to OFDMAreverse link power control processes, which will be discussed below ingreater detail.

First OFDMA Reverse Link Power Control Example

FIGS. 6A and 6B illustrate an OFDMA reverse link power control processaccording to another example embodiment of the present invention. TheOFDMA reverse link power control process of FIGS. 6A and 6B is describedbelow with respect to the hybrid CDMA/OFDMA system 300 of FIG. 3. Morespecifically, the steps of the process of FIG. 6A are described as beingperformed at the Node B 320, and the steps of the process of FIG. 6B aredescribed as being performed at the UE 305.

As shown in FIG. 6A, the Node B 320 analyzes a received signal spectrumto obtain a measure of a “total” OFDMA interference in step S600.Generally, step S600 can be interpreted as an outer-cell interferencemeasurement, because OFDMA is characterized as having a relatively lowin-cell interference measure. In an example, a majority of the measuredOFDMA interference resides within the OFDMA zones of the bandwidthallocation 400 of FIG. 4.

In step S605, the Node B 320 again analyzes the received signal spectrumto obtain a measure of the CDMA interference. It will be appreciatedthat the measured CDMA interference can be either a pre- orpost-interference cancellation (IC) measurement. In an example, if themeasurement of the CDMA interference is performed with post-interferencecancellation, the Node B 320 measures the CDMA signal spectrum prior tointerference cancellation, and then measures the residualinterference-to-total interference ratio after the interferencecancellation. The ratio of these two quantities is a measure of thepost-interference cancellation CDMA interference.

The Node B 320 uses the measured OFDMA interference (step S600) and CDMAinterference (step S605) to calculate a filtered interference ratio(FIR), which is a ratio of the measured OFDMA interference to themeasured CDMA interference, in step S610. FIR calculation is well knownin the art and will not be described further for the sake of brevity.After the FIR is calculated, the Node B 320 broadcasts the calculatedFIR to all UEs within its cell in step S615 using a forward link ordownlink common channel. The broadcast of step S615 may be performed ina variety of ways. For example, a differential broadcast scheme may beemployed by the Node B 320 wherein an initial calculated FIR is sent tolistening mobile stations. Thereafter, smaller values representingdifferences between previous FIRs are sent. However, periodically thecomplete FIR is re-broadcast to account for new users entering intocommunication with the Node B 320 and/or to reduce the effects ofsignaling errors.

In an alternative example, the Node B 320 may broadcast the FIR in stepS615 separately on CDMA and OFDMA. In yet another alternative example,interference activity bits (LABs) are broadcast to mobile stations. Themeasured CDMA interference and measured OFDMA interference are comparedto respective interference thresholds. Respective IABs are set to afirst logic level (e.g., a higher logic level or “1”) if the comparisonindicates a measured interference above or equal to the threshold andare set to a second logic level (e.g., a lower logic level or “0”) ifthe comparison indicates a measured interference below the threshold. Inthis example, two separate IABs are sent by the Node B 320 to correspondto indicate whether the measured CDMA interference (step S605) and themeasured OFDMA interference (step S600) exceed a CDMA interferencethreshold and an OFDMA interference threshold, respectively.

Referring now to FIG. 6B, the UE 305 receives the broadcasted FIR instep S650. In step S655, the UE 305 calculates a power level at which totransmit for OFDMA reverse link transmissions based on the broadcastedFIR. The calculation of step S655 will now be described in greaterdetail.

The following terms are used in the example calculation of step S655:

“Γo” is the target SINR for OFDMA pilot signals;

“Γc” is the target SINR for CDMA pilot signals;

“Pc(t)” is the CDMA pilot transmit power spectral density, transmittedfrom the UE 305, at slot t;

“Po(t)” is the unconstrained OFDMA nominal pilot power per tone at slott;

“ΔI(t)” is the periodically broadcasted FIR sent by the Node B 320 atstep S615 and received by the UE 305 at step S650 at time slot t;

“I_OFDMA(t)” is the measured OFDMA interference in step S600 at slot t;and

“I_CDMA(t)” is the measured CDMA interference in step S605 at slot t.

With the above assumptions, the filtered FIR sent by the Node B 320 atstep S615 and received by the UE 305 is expressed asΔI(t)=10 log 10[I _(—) OFDMA(t)/I _(—) CDMA(t))   Equation 3

The target SINR ratio ΔΓ is given by:ΔΓ=Γo/Γc   Equation 4

The UE 305 may thereby adjust the OFDMA pilot power per tone Po(t) asfollows:Po(t)=α(t)*Pc(t)   Equation 5

wherein α(t) is a calculated power ratio, expressed asα(t)=ΔΓ*10^(Δ(t))/10)   Equation 6

Returning to FIG. 6B, the UE 305 transmits OFDMA signals within theOFDMA zones in accordance with the calculated power level or Po(t) instep S660.

A readily apparent advantage in the above-described OFDMA reverse linkpower control process of FIG. 6A/6B is that the conventional “fast”OFDMA power control wherein dedicated control bits are sent toparticular UEs is avoided with the “broadcast” nature of the exampleapproach. Thereby, processing is offloaded from the Node Bs to the UEsfor calculating OFDMA reverse link power adjustments, which conservessystem resources.

Second OFDMA Reverse Link Power Control Example

Generally, CDMA transmissions within the CDMA zones of the bandwidthallocation 400 of the hybrid CDMA/OFDMA system 300 of FIG. 3 can be saidto be “continuous” while OFDMA transmissions with the correspondingOFDMA zones can be said to be “bursty” (e.g., infrequent,non-continuous, periodic, etc.). Conventional OFDMA power controls donot adjust OFDMA power settings during the “gaps” between OFDMAtransmission bursts. An example will now be given wherein CDMAsignaling, which is more or less continuous, is used to adjust OFDMApower controls during lapses of transmissions between OFDMA bursts.

In the following example, the definitions set forth in the descriptiongiven above with respect to the calculation of step S655 of FIG. 6B arehereby incorporated by reference.

FIG. 7 illustrates an OFDMA reverse link power control process accordingto another example embodiment of the present invention.

In step S700, the UE 305 has established a connection with the Node B120 and is transferring data via CDMA protocols within the CDMA zones ofthe bandwidth allocation 400 of the hybrid CDMA/OFDMA system 300 of FIG.3. In step S700, it is assumed that no OFDMA bursts have yet occurred.An “initial” OFDMA pilot transmit power, that is, an OFDMA pilottransmit power level established before a first OFDMA for use in thefirst OFDMA burst, is established in step S705 at the UE 305, and isexpressed byPo(t)=α(t)*Pc(t)   Equation 7wherein the initial power ratio α(t) is set to a default leveldetermined by a system engineer.

The transmit power level for “initial” OFDMA traffic levels is eitherestablished by multiplying Po(t) with a rate-dependent traffic-to-pilotratio (TPR) or by defining a pilot boost value that is rate-dependent.Here, “rate-dependent” means that the TPR or pilot boost values arebased on different SINR requirements associated with differenttransmission rates.

In step S710, the UE 305 transmits OFDMA data on one or more of theOFDMA zones. The Node B measures the SINR for the received OFDMA burstin step S715 and compares the measured OFDMA SINR with a target OFDMASINR in step S720. The target OFDMA SINR may be a fixed value, anadaptive value, etc.

If the hybrid CDMA/OFDMA system 300 allows an independent OFDMA bit forpower adjustments, the Node B 320 sends the independent OFDMA bit instep S725. Alternatively, if no such independent OFDMA bit provision isprovided in the hybrid CDMA/OFDMA system 300, the SINRs are estimatedsimultaneously in step S725. In other words, a single power control bitor common bit is used to adjust both CDMA and OFDMA transmissions at theUE 305. The common bit is determined based on both the OFDMA and CDMASINRs.

The OFDMA burst beginning in step S710 ends at step S730. During the gapbetween OFDMA bursts, the Node B 320 estimates the OFDMA SINR in stepS735 using the expressionΓo, est(t)=Γc(t)*α_(est)(t)*β(t)   Equation 8wherein Γo, est(t) is an estimated OFDMA SINR for a slot t, α_(est)(t)is an estimated power ratio for the slot t, and β(t) is a correlationfactor for the slot t.

The estimated OFDMA SINR Γo, est(t) is compared to the target OFDMA SINRro in step S740, and the Node B 320 sends an OFDMA transmit powercontrol (TPC) bit to the UE 305 in step S745 based on the comparison. ATPC bit is a single bit binary indicator, which is set to a first logiclevel (e.g., a higher logic level or “1”) to instruct a UE (e.g., UE305) to increase transmission power by a fixed amount and a second logiclevel (e.g., a lower logic level or “0”) to instruct a UE (e.g., UE 105)to decrease transmission power by the fixed amount. In an example, ifthe comparison of step S745 indicates that the estimated OFDMA SINR isless than the target OFDMA SINR, the Node B 320 sends a TPC bit havingthe first logic level (e.g., a higher logic level or “1”) to the UE 305.Otherwise, the Node B 320 sends a TPC bit having the second logic level(e.g., a lower logic level or “0”) to the UE 305.

While the estimated OFDMA SINR Γo, est(t) is not used during OFDMAbursts because actual measured OFDMA SINR values are available, thecorrelation factor β(t), used during OFDMA burst gaps, is updated duringthe OFDMA bursts to make the estimated OFDMA SINR Γo, est(t) moreaccurate during OFDMA gaps. Accordingly, the correlation factor β(t) isupdated in step S750 during OFDMA bursts with the following expressionβ(t)=(1−λ)*β(t−1)+λ*Γo(t)/(Γc(t)*α_(est)(t))   Equation 9wherein λ is a forgetting factor between 0 and 1. The forgetting factoris a constant value determined by a system engineer.

Maximum Mobile Station Transmit Power

An example of establishing a maximum power per tone threshold for the UE305's transmissions will now be described. In an example, UEs locatednear edges or boundaries of cells (e.g., between Node B 120 and Node B125) have more affect on neighboring cell's interference as compared toUEs located in close proximity to a serving Node B (e.g., near acentered position of the cell). If no control is maintained on the peakpower with which a given UE may transmit, overall system interferencemay increase. The following example of establishing a peak power pertone or maximum transmit power level for a UE within the hybridCDMA/OFDMA system 300 of FIG. 3 is given as a function of the UE'slocation with respect to a plurality of cells. Further, while the belowexample embodiments are described with respect to the UE 305 having theNode B 320 as a serving Node B and the Node B 325 as a neighboring NodeB, this particular arrangement is given for example purposes only and itwill be readily apparent that the below maximum transmit power controlprocess may alternatively be applied at any UE within the hybridCDMA/OFDMA system 300.

Each of the Node Bs (e.g., Node Bs 120, 125, etc.) within the hybridCDMA/OFDMA system 300 periodically measures an amount of receivedouter-cell interference (e.g., interference from cells other than a NodeB's own cell). Each of the Node Bs compares the measured outer-cellinterference with an outer-cell interference threshold Io_(thresh). Inan example, the RNC 330 may set the outer-cell interference thresholdIo_(thresh) for the Node Bs 320/325 Each of the k Node Bs transmits(e.g., to all UEs within range, such as the UE 305) an InterferenceActivity Bit (IAB) based on the comparison. In an example, referring toa Node B “p”, if the comparison indicates that the measured outer-cellinterference is greater than the outer-cell interference thresholdIo_(thresh), then IAB(p)=1, wherein Node B p is representative of one ofthe Node Bs within the hybrid CDMA/OFDMA system 300. Otherwise, if thecomparison indicates that the measured outer-cell interference is notgreater than the outer-cell interference threshold Io_(thresh), thenIAB(p)=0. It is understood that the IABs may be transmitted from one ormore Node Bs at once such that multiple IABs may be received by a UEwithin the hybrid CDMA/OFDMA system 300, in part based on the UE'sposition relative to neighboring or serving Node Bs within the hybridCDMA/OFDMA system 300. A maximum transmit power per tone thresholdadjustment process, performed at the UEs within the CDMA system 100,taking into account the IABs transmitted by the Node Bs will now bedescribed below with respect to a representative UE 305 in FIG. 8.

FIG. 8 illustrates a process of establishing a maximum transmit powerper tone threshold for a UE's transmissions according to an exampleembodiment of the present invention. The example embodiment of FIG. 8 isdescribed below with respect to a representative UE (e.g., UE 305) and kNode Bs (e.g., Node B 120, 125, etc.) within the hybrid CDMA/OFDMAsystem 300, wherein k is an integer greater than or equal to 1. Thesteps illustrated in FIG. 8 and described below are performed at, forexample, the UE 305 of FIG. 3. The representative UE 305 is notnecessarily in active communication with more than one of the k Node Bs(e.g., although it may be, such as in soft handoff mode), but therepresentative UE 305 is capable of “listening” to or receiving signalsfrom all of the k Node Bs. Accordingly, it will be appreciated that thenumber k may vary based on the UE 305's position within the hybridCDMA/OFDMA system 300. For example, if the UE 305 is in very closeproximity to a serving Node B such as Node B 120, k typically equals 1.As the UE 305 becomes closer to an edge of a cell, k is typicallygreater than 1.

In the example embodiment of FIG. 8, in step S800, the maximum transmitpower per tone threshold of the UE 305 being served by the Node B 320 isinitialized, by the UE 305, toP _(max)(1)=Io _(thresh)/max(G(d)), d=1, . . . , k   Equation 10wherein P_(max)(1) denotes a maximum power for an initial time period,Io_(thresh) denotes an outer-cell interference threshold (e.g., anamount of outer-cell interference that can be tolerated), and G(d)denotes an average channel gain from the UE 305 to a dth Node B amongthe k Node Bs, wherein d is an integer from 1 to k. In an example, theG(d) measurements are based on SINR measurements on the common pilot andpreamble, and the outer-cell interference threshold IOthrsh isdetermined by a design engineer.

The UE 305 receives the LABs (discussed above prior to FIG. 8) from eachof the k Node Bs in step S805 and determines whether an adjustment tothe maximum transmit power per tone threshold is required in step S810.If step S810 determines that an adjustment is necessary, a poweradjustment is calculated for the UE 305 in step S815. Otherwise, theprocess returns to step S805. In step S815, the UE 305 establishes atoken bucket for the transmission power resource called Pc_(bucket)(t),which denotes the instantaneous updated value of the transmit powerresource based on the received IABs, expressed asPc _(bucket)(t)=Pc _(bucket)(t−1)−ΔP _(down)   Equation 11if any of the LABs received by the UE 305 are set to “1”, whereinΔP_(down)=w* max(G(y)), wherein y denotes y Node Bs among the k Node Bswhich are sending the IAB equal to “1” at time t, and w is a fixedweight factor determined by a design engineer.

Pc_(bucket)(t) is alternatively expressed asPc _(bucket)(t)=Pc _(bucket)(t−1)+ΔP _(up)   Equation 12if all of the IABs received by the UE 305 are set to “0”, wherein “t”denotes a current time period and “t−1” denotes a previous time period,and ΔP_(up) is expressed byΔP _(up) =[x/(1−x)]ΔP _(down)wherein x is equal to the probability that the outer-cell interferencemeasured by a given Node B is greater than the outer-cell interferencethreshold IO_(thresh). In an example, the probability “x” is based on acoverage requirement for the given Node B (e.g., Node B 320). In afurther example, the probability “x” is determined during deployment orinstallation of the hybrid OFDMA/CDMA system 300.

P_(bucket)(t) is an averaged version of Pc_(bucket)(t), and is expressedasP _(bucket)(t)=P _(bucket)(t−1)+Pc _(bucket)(t)−P _(max)(t−1)   Equation13

P_(max)(t) evaluates toP _(max)(t)=min(P _(max)(t−1), P _(bucket)(t))   Equation 14

if a new encoder packet is scheduled for transmission from the UE 305 tothe Node B 320, andP _(max)(t)=P _(bucket)(t)−P _(margin)   Equation 15

if a new encoder packet is not scheduled for transmission, whereinP_(margin) is an offset value which is greater than or equal to 0 toensure the bucket does not become empty during the transmission of theencoder packet. In an example, a data rate for the new encoder packet isselected such that P_(max)(t) is set to a sufficient power level so asto achieve a threshold level of spectral efficiency.

Once the maximum transmit power per tone threshold P_(max)(t) is set inaccordance with one of Equations 14 and 15 in step S815, the processreturns to step S605.

Accordingly, with the above example methodology described with respectto FIG. 8, one of ordinary skill in the art will appreciate that UEscloser to a greater number of Node Bs (e.g., further away from a servingNode B and closer to cell edges) adjust the maximum transmit power pertone threshold with larger steps, whereas UEs closer in proximity to theserving Node B react more slowly to the IAB bits. The combination of thepilot reference power (Po(t)) and the maximum allowed data/pilot powermay be used in the computation of the spectral efficiency as requestedby the UE.

Further, an alternative example of establishing and adjusting a CDMAmaximum transmit power per chip threshold is described in US PatentApplication UNKNOWN#, entitled “METHODS OF REVERSE LINK POWER CONTROL”,filed concurrently with this application by the inventors of the subjectapplication, hereby incorporated by reference in its entirety.

Example embodiments of the present invention being thus described, itwill be obvious that the same may be varied in many ways. For example,it is understood that a Node B and a UE may alternatively be referred toas a base station (BS) or access network (AN) and a mobile station (MS),access terminal (AT) or mobile unit (MU), respectively. Further, whileabove described with respect to CDMA/OFDMA systems, it will be readilyapparent how the same may be adapted for use in UMTS systems.

Such variations are not to be regarded as a departure from the exampleembodiments of the invention, and all such modifications are intended tobe included within the scope of the invention.

1. A method of controlling reverse link transmission power in a wirelesscommunications network, comprising: first measuring a first type ofinterference; second measuring a second type of interference; andbroadcasting information from which a ratio between the first and secondmeasurements may be determined.
 2. The method of claim 1, wherein thefirst type of interference is OFDMA interference.
 3. The method of claim1, wherein the second type of interference is CDMA interference.
 4. Amethod of controlling reverse link transmission power in a wirelesscommunications network, comprising: receiving broadcasted informationfrom which a ratio between two different types of interference may bedetermined; and calculating a power level for reverse link transmissionsbased on the received-broadcasted information.
 5. The method of claim 4,wherein the two different types of interference are CDMA interferenceand OFDMA interference.
 6. The method of claim 4, further comprising:transmitting at least one signal at a transmission power level equal tothe calculated power level.
 7. A method of controlling reverse linktransmission power in a wireless communications network, comprising:first adjusting OFDMA transmission power based on first feedback signalsduring an OFDMA transmission; and second adjusting OFDMA transmissionpower based on second feedback signals during periods between OFDMAtransmissions.
 8. The method of claim 7, wherein the first feedbacksignals are based on a measured OFDMA SINR and the second feedbacksignals are based on an estimated OFDMA SINR.
 9. A method of controllingreverse link transmission power in a wireless communications network,comprising: sending first power adjustment indicators based on measuredOFDMA SINRs when receiving OFDMA transmissions from a mobile station;and sending second power adjustment indicators based on estimated OFDMASINRs when not receiving OFDMA transmissions from the mobile station.10. The method of claim 9, wherein the estimated OFDMA SINRs are basedon (i) previous OFDMA transmissions and (ii) CDMA transmissions receivedafter (i).
 11. A method of determining a maximum permitted transmissionpower level, comprising: receiving a plurality of interferenceindicating signals from different base stations; and determining whetherto adjust a maximum transmit power threshold based on the plurality ofinterference indicating signals, the maximum transmit power thresholdindicating the maximum permitted transmission power level below whichtransmissions are constrained.
 12. The method of claim 11, furthercomprising: increasing the maximum transmit power threshold if at leastone of the plurality of interference indicating signals indicates anouter-cell interference exceeding an outer-cell interference threshold;and decreasing the maximum transmit power threshold if the plurality ofinterference indicating signals do not include at least one interferenceindicating signal indicating an outer-cell interference exceeding theouter-cell interference threshold.
 13. The method of claim 12, whereinthe decreasing step decreases the maximum transmit power threshold by afixed amount.
 14. The method of claim 12, wherein the increasing stepincreases the maximum transmit power threshold by a fixed amount. 15.The method of claim 11, wherein the maximum transmit power threshold isassociated with one of a power per tone and a power per chip.
 16. Themethod of claim 1, further comprising: Determining a ratio between thefirst and second measurements.
 17. The method of claim 17, wherein thebroadcasted information is the determined ratio.
 18. The method of claim11, wherein the received information is the broadcasted ratio.